Previous workers have found that the concentration of urea in human sweat exceeds the concentration of urea in plasma. This fact has been confirmed in the present work and extended by measurements of the concentrations of urea in the sweat and the corresponding concentrations of urea in the plasma over a range of 25- fold variation in the latter. An analysis of the data showed that the ratio of the concentration of urea in sweat to the concentration of urea in plasma, S/P, was independent of the plasma concentration, independent of the absolute flux of urea or water, and independent of the calculated energy expenditure. Two experiments showed that the concentration of urea in sweat followed a rising concentration in plasma with a time lag of approximately 5 minutes; this fact indicates that the accumulation of urea in sweat is a continuous process which is in operation during the observed discharge. These observations suggest that urea is carried into the gland in some precursor solution and subsequently raised to a higher concentration by the reabsorption from this solution of a constant fraction of the water.

Blood↗

PubMed1953

Variation in the functional power of human sweat glands.

A method has been worked out for the measurement of the volume of sweat produced by individual glands. A special paper, impregnated with iodine, absorbs water in a uniform way and shows the area of wetting by a sharply defined blue dot. Indirect calibrations showed that 1 cm.(3) of water would form a spot of 700 cm.(2) area, and that this relation of volume to area was a constant one over a wide range. The actual volumes encountered in prints of the sweat glands were from 5 x 10(-9) to 4 x 10(-6) cm.(3). The relative activity of glands at any instant of time can be expressed by the statistical distribution of log diameter of the dots on the print. This distribution, which might at first sight seem rather artificial, has the advantage of being unaffected by a proportionate change in the output of water from each gland. Thus it is independent of the duration of contact between print paper and skin, and of changes in the average flow from the field as a whole. It is sensitive only to changes in the activity of glands relative to each other. The methods of printing and statistical analysis were used to study the relative activity of glands in a field of 22 mm. diameter. Glands of the forearm and back were studied both under direct stimulation with mecholyl and under the reflex stimulation of environmental heat, similar results being obtained with the two kinds of stimuli. Glands of the abdomen and leg, stimulated with mecholyl, were studied in one experiment. Detailed comparison of the dots in consecutive prints showed that the large dots remained large and the small dots continued to be small. These persistent differences in the outflow of water from adjacent glands were interpreted as being due to differences in the functional power of the glands. Repeated prints of the glands during a period of 75 minutes, in which the sweat flow was declining, showed that the relative activity of the glands remained constant. This meant that the set of glands, although differing greatly in power, varied together as a functional unit. Different regions of the body show not only the variation of glandular power within each small area, but also marked differences in the average power of glands belonging to the different regions. Glands of the back, for instance, show a much greater outflow than glands of the forearm when stimulated equally with a local injection of mecholyl. Equal rates of outflow, therefore, do not mean equal states of functional activity, unless the regions being compared are of equal functional power.

Hot Temperature↗

PubMed1953

The permeability of human sweat glands to a series of sulfonamide compounds.

A series of sulfonamide compounds, para-aminohippurate, and inulin were used to study the permeability of the epithelium of human sweat glands. Inulin was not excreted in the sweat. The ratios of the concentrations in sweat to the concentrations in plasma, S/P, of sulfanilamide, sulfapyridine, sulfathiazole, sulfadiazine, and para-aminohippurate were found to be 0.69, 0.58, 0.13, 0.11, and 0.02 respectively, independent of the plasma concentrations and the sweating rates. The fact that the S/P ratios are thus unaffected by the absolute number of molecules transported suggests that these compounds enter into the sweat by simple diffusion and not via a specific secretory mechanism which could become saturated by increasing load. If this is so, the difference in the S/P ratios must be explained by an unequal permeability of the epithelium of the sweat gland to the various compounds and some explanation for these differences in the rate of excretion must exist in terms of physicochemical properties of the compounds. A comparison between the S/P ratios and the pK values of the various sulfonamides indicates that the differences in their rates of excretion in the sweat depend upon the degree of ionization of the various compounds at the physiological pH. Compounds which are mainly non-ionized are excreted with high S/P ratios, whereas ionized compounds appear with low ratios. A quantitative relationship was shown to exist between the S/P ratio for each compound and the percentage of the compound which is non-ionized at pH 7.4.

Humans↗